The present invention relates to a new magnetoresistive effect type reproducing head, and a recording-reproducing separation type magnetic head, a head disk assembly and a magnetic disk apparatus, which use the reproducing head.
A magnetoresistive effect type reproducing head using a magnetoresistive effect or a giant magnetoresistive effect is made of a magnetic multi-layer film, which exhibits the magnetoresistive effect or the giant magnetoresistive effect, a magnetoresistive effect type element including electrodes provided at both sides of the magnetic multi-layer film, and magnetic shield films arranged at the upper and lower sides of the magnetoresistive effect type element.
A principle of magnetic field detection using a magnetoresistive effect type element is based on use of a phenomena in which the electrical resistance of a magnetic multi-layer film changes corresponding to the strength of a magnetic field applied to the magnetic multi-layer film, which possesses a magnetoresistive effect or a giant magnetoresistive effect. Further, changes in the applied magnetic field are defected by causing a current to flow in the magnetic multi-layer film and then measuring the potential difference generated across the magnetic multi-layer film. However, this principle is well known.
In reproducing a stray magnetic field from information magnetically recorded in a magnetic disk installed in a magnetic disk apparatus, it is well known to cover the upper and lower sides of a magnetoresistive effect type element with magnetic shield films via an insulating layer in order to improve the spatial resolution and reduce the effects of magnetic field leakage, such as from a motor and so on, which tends to cause noise.
For development of a method of more densely recording information in a magnetic disk apparatus, in order to improve the spatial resolution, it has been tried and is also well known to reduce the distance between an upper magnetic shield and a lower magnetic shield, that is, the magnetic gap of a reproducing head. Further, conventionally, 80Ni--Fe permalloy, Fe--Al--Si Sendust, Co noncrystalline magnetic material, etc., are mainly used for a magnetic shield film. Further, Japanese Patent Laid-Open 124121/1996 discloses a magnetic shield of Ni--Fe--P alloy or Ni--Fe--B alloy that is formed by an electroplating method.
A magnetoresistive effect type reproducing head has a structure in which a magnetoresistive effect type clement is formed on a lower magnetic shield via an insulation film, and an upper magnetic shield is also formed on the magnetoresistive effect type element via an insulation film.
In order to satisfy the requirement for a high increase in the recording density, especially, the linear recording density, in a magnetic disk apparatus, the distance between the lower magnetic shield and the upper magnetic shield is reduced to improve the spatial resolution. For this purpose, the thickness of the respective insulation films between a magnetoresistive effect type or giant magnetoresistive effect type element and each of the upper and lower magnetic shields is largely reduced. Thus, the withstand voltage between the magnetoresistive effect type element and the respective upper and lower magnetic shields tends to be easily deteriorated. It is believed that the deterioration of the withstand voltage in the insulation films is caused by pin holes in the insulation films.
The respective resistivities .rho. of a 80Ni--Fe permalloy film, a Fe--Al--Si Sendust film, and a Co--Nb--Zr alloy film, which are conventionally used for the upper and lower magnetic shield films, is approximately 20 .mu..OMEGA..multidot.cm, 80 .mu..OMEGA..multidot.cm, and 100-150 .mu..OMEGA..multidot.cm, respectively. On the other hand, the average resistivity .rho. of a sensor part in a magnetoresistive effect type element, although the resistivity depends on the composition of the sensor part, is approximately 20-100 .mu..OMEGA..multidot.cm. That is, the resistivity of the sensor part in a magnetoresistive effect type element is approximately the same as that of the magnetic shields. Moreover, since the thickness of the sensor part in a magnetoresistive effect type element is about 50 nm, and the thickness of the magnetic shields is about 1-3 nm, the resistance of the sensor part in a magnetoresistive effect type element is less than 1/20 of that of a corresponding region in each magnetic shield. Therefore, if the magnetic gap is reduced, it is possible that current will leak from a pin hole generated in a part, such as a boundary region between each electrode and the sensor part in a magnetoresistive effect type element, at which the thickness of the gap is large and the thickness of the insulation film tends to become thin, and an insulation break-down of the magnetoresistive effect type element is caused by such a current leakage. Even if the current leakage occurs without an element break-down, since the resistance of the sensor part in a magnetoresistive effect type element is less than 1/20 of that of a corresponding region in each magnetic shield, the largest amount of current flows into the magnetic shields, and information reproduction by the magnetoresistive effect type element becomes impossible. This problem is an inevitable result of reducing the magnetic gap of the presently used structure in a magnetoresistive effect type element.